US First Lady Michelle Obama has launched a scathing attack on Donald Trump over his "demeaning" remarks about women, saying the Republican Presidential nominee's "sexually predatory behaviour" has left her "shaken" to the core.

"The fact is that in this election, we have a candidate for President of the US who, over the course of his lifetime and the course of this campaign, has said things about women that are so shocking, so demeaning that I simply will not repeat anything here today," she said at an election rally in Manchester, New Hampshire yesterday.

"Last week, we saw this candidate actually bragging about sexually assaulting women. And I can't believe that I'm saying that a candidate for President of the United States has bragged about sexually assaulting women," Michelle said in an impassioned campaign speech without taking the name of Trump.

Noting that she cannot stop thinking about the remarks, 52-year-old Michelle said it had "shaken me to my core in a way that I couldn't have predicted."

"While I'd love nothing more than to pretend like this isn't happening, and to come out here and do my normal campaign speech, it would be dishonest and disingenuous to me to just move on to the next thing like this was all just a bad dream," she said.

Michelle said this was not something that one can ignore.

"It's not something we can just sweep under the rug as just another disturbing footnote in a sad election season. Because this was not just a 'lewd conversation. This wasn't just locker-room banter,'" she noted.

"This was a powerful individual speaking freely and openly about sexually predatory behaviour, and actually bragging about kissing and groping women, using language so obscene that many of us were worried about our children hearing it when we turn on the TV," she added.

Observing that it seems that the case is not an isolated incident, Michelle said it is one of countless examples of how he has treated women his whole life.

"I have to tell you that I listen to all of this and I feel it so personally, and I'm sure that many of you do too, particularly the women. The shameful comments about our bodies. The disrespect of our ambitions and intellect. The belief that you can do anything you want to a woman," she said.

"It is cruel. It's frightening. And the truth is, it hurts. It hurts. It's like that sick, sinking feeling you get when you're walking down the street minding your own business and some guy yells out vulgar words about your body. Or when you see that guy at work that stands just a little too close, stares a little too long, and makes you feel uncomfortable in your own skin," Michelle said.

It's that feeling of terror and violation that too many

women have felt when someone has grabbed them, or forced himself on them and they've said no but he didn't listen - something that happens on college campuses and countless other places every single day, she said.

It reminds us of stories we heard from our mothers and grandmothers about how, back in their day, the boss could say and do whatever he pleased to the women in the office, and even though they worked so hard, jumped over every hurdle to prove themselves, it was never enough, Michelle said.

"We thought all of that was ancient history, didn't we? And so many have worked for so many years to end this kind of violence and abuse and disrespect, but here we are, in 2016, and we're hearing these exact same things every day on the campaign trail," she said.

"We are drowning in it. And all of us are doing what women have always done: We're trying to keep our heads above water, just trying to get through it, trying to pretend like this doesn't really bother us maybe because we think that admitting how much it hurts makes us as women look weak. Maybe we're afraid to be that vulnerable," she said.

"Maybe we've grown accustomed to swallowing these emotions and staying quiet, because we've seen that people often won't take our word over his. Or maybe we don't want to believe that there are still people out there who think so little of us as women. Too many are treating this as just another day's headline, as if our outrage is overblown or unwarranted, as if this is normal, just politics as usual," she added.

Michele said this was not normal and not politics as usual, but "disgraceful" and "intolerable."

"It doesn't matter what party you belong to - Democrat, Republican, independent - no woman deserves to be treated this way. None of us deserves this kind of abuse," she said.

"I know it's a campaign, but this isn't about politics. It's about basic human decency. It's about right and wrong. We simply cannot endure this, or expose our children to this any longer - not for another minute, and let alone for four years. Now is the time for all of us to stand up and say enough is enough. This has got to stop right now," she said amidst applause from the audience.